1. Field of the Invention
The invention relates to an arrangement of holes for forming a cooling film on a component wall subjected to a flow of hot gas, the component being in particular a turbine vane or blade or a combustion chamber of a gas turbine,
2. Discussion of Background
The publication "Journal of Engineering for Power", April 1978, Vol. 100, Pages 303 to 307, reveals a test set-up for the simulation of a cooling film, in which a flat plate is provided with holes which represent the ejection openings of tubes set at an angle of 35.degree. relative to the plane of the plate. The holes are arranged in the form of two rows which are staggered and laterally offset relative to the main flow direction.
The series of tests described in this article indicate a marked increase in the cooling effect relative to an individual row of holes. This effect is attributed to the fact that the jets of cooling air emerging from the first row deflect the cooling air jets emerging from the second row onto the surface of the wall to be cooled and, by this means, increase their cooling effectiveness. In addition, the cooling film of the first row of holes forming further downstream is located above the cooling film of the row of second holes and additionally protects the latter from the penetration of hot gas.
DE 35 08 976 A1 shows a turbine vane or blade which, because of the high level of thermal loading, is provided with a plurality of rows of holes in order to form cooling films. In the stagnation point region and adjacent to it on the suction surface, three adjacently located rows of holes are provided in each case in order to further increase the cooling effect in these particularly highly thermally loaded wall portions of the turbine vane or blade. In this arrangement, it is accepted that the cooling air requirement is increased because of the many rows of holes.
A similar direction is indicated by the turbine vane or blade known from EP 0 501 813 B1 in which various variants of hole arrangements in a double row are proposed for the formation of a cooling film. One of the variants proposes allocating two holes of small diameter in the first row to each hole of larger diameter in the second row. The association of the holes in the first row with the respective holes in the second row follows from the fact that these are configured as flow branches of a common inlet opening.
Disadvantageous in this solution is again the high consumption of cooling air, which is caused by the large number of outlet openings in the first row. A further disadvantage may be considered as being the low flexibility in the selection of the direction of the individual holes because the latter start from a single, common inlet hole. In particular, the cooling air jets emerging from the holes in the first row have directional components extending in different directions which point laterally, i.e. at right angles to the main flow, which is undesirable in many cases.